Micropower Synchronous Buck-Boost DC/DC Converter for WCDMA Applications

The LTC3444 is a highly efficient, fixed frequency, buck-boost DC/DC converter, which operates from input voltages above, below, and equal to the output voltage. The topology incorporated in the IC provides a continuous transfer function through all operating modes, making the product ideal for a single Lithium-Ion or multi-cell applications where the output voltage can vary over a wide range.

The LTC3444 has been optimized for use in 3G WCDMA applications. A unique design yields high efficiency at very low output voltages while also eliminating external components. The high speed error amplifier provides the fast transient response required to slew the RF power amplifier from standby to transmit and transmit to stand by power levels. Output overvoltage protection protects the RF power amplifier.

Operating frequency is internally set to 1.5MHz to minimize external component size while maximizing efficiency.

Other features include <1μA shutdown current, internal soft-start, peak current limit and thermal shutdown. The LTC3444 is available in a small, thermally enhanced 8-lead (3mm × 3mm) DFN package.

Applications

* WCDMA Applications–3G Handsets with High Speed Data Rate Capability

* MP3 Players

* Digital Cameras

* Optimized Features for WCDMA Handsets

* Regulated Output with Input Voltages Above, Below, or Equal to the Output

* 0.5V to 5V Output Range

* Up to 400mA Continuous Output Current From a Single Lithium-Ion Cell

* Minimal External Components

* 1.5MHz Fixed Frequency Operation

* Internal Loop Compensation for Fast Response <25μs Full Scale Output Slewing; COUT 4.7μF

* Output Disconnect in Shutdown

* 2.75V to 5.5V Input

* <1μA Shutdown Current

* Internal Soft-Start

* Output Overvoltage Protection

* Single Inductor, No Schottky Diodes Required

* Small, Thermally Enhanced 8-Lead (3mm × 3mm) DFN Package